1. Field of the Invention
The present invention relates to smart cards, especially to contactless and dual interface smart cards, and to methods for producing and enhancing such smart cards to extend the communication distance where the smart card can be used reliably.
2. Description of the Related Art
Having the same size as a credit card, a smart card is able to store and process information by means of the electronic circuits of a chip embedded into the plastic body of the smart card. This chip also contains the processor, volatile memory, non-volatile memory and I/O support. A smart card therefore is a portable and tamper resistant computer. Unlike magnetic stripe cards, smart cards carry both processing power and information. The physical appearance and properties of a smart card are defined in ISO 7816, part 1.
Usually, a smart card does not contain a power supply, a display or a keyboard but communicates with the outside world through a card acceptance device. Therefor, there are two different communication concepts:
Contact communication using gold contacts on the front of the card that are attached to the chip within the card body. Such “contact cards” have to be inserted correctly, i.e. with a defined orientation, into a mechanical card acceptance device.
Contactless communication using electromagnetic fields and an antenna that is attached to the chip within the card body. Such “contactless cards” have only to be placed in a certain proximity of an appropriate card acceptance device to be able to communicate.
As contactless smart cards are very easy to handle, they are popular in situations requiring fast transactions. Public transport systems and access control for buildings are exemplary applications for contactless smart cards. Besides, the microcircuit of contactless smart cards is fully sealed inside the card. In consequence, there are no contacts to become worn from frequent use which is another reason why contactless smart cards overcome limitations of contact cards.
Despite the advantages of contactless smart cards, these cards have their own drawbacks. As mentioned above, contactless smart cards must be located within a certain proximity to exchange data with the card acceptance device and to collect power from the electromagnetic field emitted by the card acceptance device. As the card may move out of range very quickly, only limited data can be transmitted and the transmitted data may be intercepted without the cardholder realizing it. That is why contactless smart cards only qualify for transactions with relatively short duration.
On contactless smart cards that carry two or more chips using the same antenna (e.g. a Mifare and a Legic chip) or that have two or more antennas (e.g. a JavaCard dual interface chip and a Legic chip), this problem is even worse. Two chips attached to one antenna or two different antennas on one card will one another reduce the communication distance. The power that is available from the electromagnetic field emitted by the card acceptance device will be lower compared to a situation where only one consumer will draw power from this field. This problem applies to data communication, too. Due to interference from the second chip or antenna, the effective data rate will be lower compared to a situation where only one consumer will draw power from the field emitted by the card acceptance device.